JP2017506297A - Turbine component with negative CTE characteristics - Google Patents

Abstract

The turbine component (10) has opposing inner and outer surfaces, a metal wall configured to direct the combustion gas flow of the gas turbine engine, and a metal rigidly attached to one of the surfaces With negative CTE structure (48, 50, 54) made of. [Selection] Figure 1

Description

  The present invention relates generally to turbine components, and more particularly to turbine components used in high temperature environments.

  A typical gas turbine engine includes a turbomachine core having a high pressure compressor, a combustor, and a high pressure turbine in series flow relationship. The core can be operated in a known manner to produce a primary gas stream. The high pressure turbine includes one or more stages that extract energy from the primary gas stream. Each stage includes a fixed turbine nozzle in front of a downstream rotor carrying turbine blades. These “hot parts” parts operate in extremely hot environments that promote thermal corrosion and oxidation of metal alloys.

  In the prior art, hot zone parts are typically cast from nickel or cobalt based alloys with good high temperature creep resistance, conventionally known as “superalloys”. Such alloys are primarily designed to meet mechanical property requirements such as creep rupture strength and fatigue strength. The casting process is controlled to produce the desired microstructure, eg, directional solidification (“DS”) or single crystal (“SX”). Single crystal microstructure refers to a structure without crystallographic grain boundaries. Single crystal casting requires careful control of the seed element (ie, the nucleation cooling point) and the temperature during cooling. However, the production of such a structure is expensive and the production yield is relatively low.

  Accordingly, there is a need for gas turbine engine components that have higher high temperature creep resistance and stress rupture resistance.

European Patent Application No. 2620240

  The present invention addresses this need by providing a metal part that incorporates a negative coefficient of thermal expansion ("CTE") structure.

  In accordance with one aspect of the present invention, a turbine component is rigid to one of the above surfaces and a metal wall that has opposing internal and external surfaces and is configured to direct the combustion gas flow of a gas turbine engine. With a metal negative CTE structure attached to.

  According to another aspect of the invention, the negative CTE structure is firmly attached to the internal surface.

  According to another aspect of the invention, the negative CTE structure is integrally formed with the metal wall.

  According to another aspect of the invention, the metal wall forms part of a gas turbine engine airfoil.

  According to another aspect of the invention, the metal wall is a pressure or suction side wall of the airfoil.

  According to another aspect of the invention, the negative CTE structure comprises a repeating array of hexagonal cells.

  According to another aspect of the present invention, the negative CTE structure includes a repetitive two-dimensional array of generally hourglass-shaped cells, each cell having two spaced concave surfaces joined by two spaced convex walls. Has a wall.

  According to another aspect of the present invention, the negative CTE structure includes a repeating two-dimensional array of cells having a rectangular shape.

  According to another aspect of the present invention, the wall includes opposing spaced outer layers, and a negative CTE structure fills the space between the outer layers.

  According to another aspect of the present invention, a method for fabricating a part comprising placing a metal powder in a work plane; directing a beam from a directional energy source to accommodate a cross-sectional layer of the part Fusing the powder according to a pattern; periodically repeating the placing and fusing steps to build a wall for each layer, the wall having opposing inner and outer surfaces, the wall being a gas A method is provided that is configured to direct a combustion gas flow of a turbine engine; and forming a metallic negative CTE structure integrally with one of the surfaces.

  According to another aspect of the invention, the negative CTE structure is integrally formed with the internal surface.

  According to another aspect of the invention, the wall is a pressure sidewall or suction sidewall of a gas turbine engine airfoil.

  According to another aspect of the invention, the negative CTE structure comprises a repeating array of hexagonal cells.

  According to another aspect of the present invention, the negative CTE structure includes a repetitive two-dimensional array of generally hourglass-shaped cells, each cell having two spaced concave surfaces joined by two spaced convex walls. Has a wall.

  According to another aspect of the present invention, the negative CTE structure includes a repeating two-dimensional array of cells having a rectangular shape.

  According to another aspect of the invention, the wall includes opposing spaced outer layers, and a negative CTE structure fills the space between the outer layers.

  The invention can best be understood with reference to the following description taken in conjunction with the accompanying drawings.

1 is a schematic perspective view of an exemplary turbine component constructed in accordance with aspects of the present invention. FIG. FIG. 3 is a schematic diagram of an exemplary negative CTE structure. FIG. 3 is a schematic diagram of another exemplary negative CTE structure. FIG. 3 is a schematic diagram of another exemplary negative CTE structure. It is a schematic sectional drawing of the turbine component of FIG. FIG. 6 is a view taken along line 6-6 of FIG. It is a partial section schematic side view of the additive manufacturing apparatus constructed | assembled by the aspect of this invention. FIG. 8 is a view taken along line 8-8 in FIG. 7. It is a partial section schematic side view of the additive manufacturing apparatus constructed | assembled by the aspect of this invention. FIG. 10 is a view taken along line 10-10 in FIG. It is a partial section schematic side view of the additive manufacturing apparatus constructed | assembled by the aspect of this invention. FIG. 12 is a view taken along line 12-12 of FIG. FIG. 2 is a schematic plan view of a portion of a wall of a turbine component. FIG. 14 is a view taken along line 14-14 in FIG. 13.

  In the drawings, like reference numerals designate like elements throughout the various views. Referring now to the drawings, an exemplary turbine blade 10 is shown in FIG. The turbine blade 10 includes a conventional dovetail 12, which is complementary to the dovetail slot feature of a rotor disk (not shown) for holding the turbine blade 10 radially to the disk as it rotates during operation. It may have any suitable form including engaging features. The blade shank 14 extends radially upward from the dovetail 12, projects laterally outward from the shank 14 and terminates in a platform 16 surrounding the shank 14. The hollow airfoil 18 extends radially outward from the platform 16 to the hot gas stream. The airfoil has a base 20 at the connection between the platform 16 and the airfoil 18 and a tip 22 at its radially outer end. The airfoil 18 has a concave pressure sidewall 24 and a convex suction sidewall 26 joined together at a leading edge 28 and a trailing edge 30. The pressure side wall 24 and the suction side wall 26 together form a peripheral wall that surrounds the internal space, the peripheral wall having an internal surface facing the internal space, and the opposing external surfaces facing the external environment. . The airfoil 18 can take any configuration suitable for extracting energy from the hot gas stream and causing rotation of the rotor disk. The airfoil 18 may incorporate a plurality of trailing edge cooling holes 32 in the pressure sidewall 24 of the airfoil 18 or may incorporate several trailing edge bleed slots (not shown). Good. The tip 22 of the airfoil 18 may be integrated with the airfoil 18, may be formed separately, or closed by a tip lid 34 that may be attached to the airfoil 18. Yes. An upright squealer tip 36 extends radially outward from the tip lid 34 and is positioned immediately below the assembled engine stationary shroud (not shown) to minimize airflow loss through the tip 22. Located nearby. The squealer tip 36 includes a suction side tip wall 38 disposed in a spaced relationship with the pressure side tip wall 40. Tip walls 40 and 38 are integral with airfoil 18 and form extensions of pressure side wall 24 and suction side wall 26, respectively. The outer surfaces of the pressure side tip wall 40 and the suction side tip wall 38 form a continuous surface with the outer surfaces of the pressure side wall 24 and the suction side wall 26, respectively. A plurality of film cooling holes 44 pass through the outer wall of the airfoil 18. The film cooling hole 44 communicates with the internal space of the airfoil 18. As shown in FIGS. 5 and 6, the interior of the airfoil 18 may include a cooling passage defined by an inner wall 46 having a complex configuration, such as a serpentine configuration.

In order to obtain sufficient creep rupture strength and fatigue strength, and to prevent thermal corrosion and oxidation, the turbine blade 10 is made of an alloy based on nickel or cobalt, conventionally known as “superalloys”, such as Made of material with good high temperature creep resistance. All materials including such superalloys expand or contract in response to temperature changes. A material property called coefficient of thermal expansion or “CTE” relates to a change in material size (ie volume or linear dimension) with changes in temperature. Generally, CTE is expressed as α _V = 1 / V (dV / dT) or α _L = 1 / L (dL / dT), respectively, where α is CTE and V is volume. , L is the length and T is the temperature.

  Most materials, including superalloys, have a positive CTE. This means that when considering homogeneous solid masses such as rectangular solids, their dimensions increase with increasing temperature. Positive CTE is a factor that contributes to the increase in creep and the possibility of defective parts due to breakage.

  Some structures exhibit a negative CTE as a result of their geometric configuration, even if the construction material has a positive CTE. In other words, the dimensions of this structure decrease with increasing temperature. As used herein, the term “negative CTE structure” refers to any structure that exhibits these properties.

  Figures 2-4 show examples of some known structures that exhibit a negative CTE. FIG. 2 is a honeycomb structure including a repetitive two-dimensional array of cells 48, each cell 48 being a regular hexagon defined by walls 63.

  FIG. 3 is a pattern that is generally hourglass-shaped and includes a repetitive two-dimensional array of cells 50 defined by a plurality of walls 52. Each cell 50 has two walls 52 that are concave with respect to that cell 50 connected by two walls 52 ′ that are convex with respect to that cell 50. Each cell 50 is rotated 90 degrees with respect to its adjacent cell 50. As a result, each concave wall 52 of the first cell 50 also defines a convex wall 52 ′ of adjacent cells 50.

  FIG. 4 is a pattern including a repeating two-dimensional array of cells 54 having a rectangular shape.

  The airfoil 18 incorporates a negative CTE structure to provide a thermal expansion cancellation effect. Although best shown in FIGS. 5 and 6, in the illustrated example, the negative CTE structure is a hexagon described above that is integrally formed with the inner surfaces of the pressure sidewall 24 and the suction sidewall 26, respectively. Contains a pattern of cells 48. The negative CTE structure may cover all of the airfoil peripheral wall or may cover selected portions. As shown, the negative CTE structure is continuous, but may be applied to a localized area within the airfoil 18. The wall 63 defining the cell 48 has a thickness or depth “T1”, which is part of the overall thickness “T2” of the airfoil peripheral wall. When the thickness or the depth T1 is larger, it is expected that the thermal expansion canceling effect becomes larger and the bulk of the airfoil peripheral wall is further reduced. Thus, the exact thickness ratio or ratio T1 / T2 will be selected according to the requirements of the particular application. In plan view (see FIG. 2), the cell 48 has a major dimension or diameter “D”. This dimension, as well as the thickness “W” of the wall 63, will vary depending on the particular application.

  Considering only the thermal expansion canceling effect, a negative CTE structure may be placed on the outer surface of the airfoil 18, but maintaining the aerodynamic characteristics of the airfoil and heat transfer to the airfoil 18. For practical reasons such as avoidance, the negative CTE structure is preferably located on the inner surface of the airfoil peripheral wall.

  The negative CTE structure defines a “scaffold” that is firmly attached to the airfoil 18. The negative CTE structure may be a single, integral or integrated structure or element of the airfoil 18. The airfoil 18 operates in a high temperature environment and is exposed to the potential for creep and stress rupture caused by thermal and mechanical loads and the positive CTE of the base alloy. However, the negative CTE structure shrinks in response to high temperatures, thus providing a counter force that counteracts the increase in parts. This also provides a safety tolerance for component breakage.

  It should be noted that the turbine blade 10 described above is only one example of many types of components that can incorporate a negative CTE structure, generally referred to herein as “C”. Non-limiting examples of turbine components to which these principles apply include rotating airfoils (eg, blades, buckets), non-rotating airfoils (eg, turbine buckets, vanes), turbine shrouds, and combustor components Is mentioned. Each of these components has a common feature that the wall has an interior surface and an exterior surface, the wall being formed to induce or direct a combustion gas flow during operation of the gas turbine engine. .

  The negative CTE structure can also be incorporated directly into the internal structure of the component wall. For example, FIGS. 13 and 14 show a portion of wall 228, typically represented by a turbine component wall, such as pressure side wall 24 or suction side wall 26 described above. Wall 228 includes opposing spaced outer layers 230 and 232, and a negative CTE structure 234 fills the space between the outer layers.

  The component C incorporating the negative CTE structure as described above is difficult or impossible to manufacture such a small internal structure using conventional casting or machining processes, and so is the additive manufacturing method. It is particularly suitable for production using FIG. 7 schematically shows an apparatus 100 for carrying out the additive manufacturing method. The basic parts are a table 112, a powder supply 114, a scraper 116, an overflow container 118, a build platform 120 that may be surrounded by a build enclosure 122, a directional energy source 124, and a beam steering device 126. Each of these parts will be described in more detail below. The device 100 also optionally includes an external heat control device that will be described below.

  The table 112 is a rigid structure that provides a flat work surface 128. The work surface 128 is coplanar with the virtual work plane and defines a virtual work plane. In the illustrated example, the work surface 128 communicates with the building enclosure 122 and exposes the building platform 120, a central opening 130 that communicates with the powder feed 114, and an overflow opening that communicates with the overflow container 118. Part 134 is provided.

  The scraper 116 is a rigid, horizontally long structure on the work surface 128. The scraper 116 is connected to an actuator 136 that is operable to selectively move the scraper 116 along the work surface 128. The actuator 136 is shown schematically in FIG. 7 and can be used for this purpose with understanding devices such as pneumatic or hydraulic cylinders, ball screws, or linear electric actuators.

  The powder supply 114 is provided below the supply opening and includes a supply container 138 communicating with the supply opening, and an elevator 140. The elevator 140 is a plate-like structure that can slide vertically within the supply container 138. The elevator 140 is connected to an actuator 142 that is operable to selectively move the elevator 140 up and down. The actuator 142 is shown schematically in FIG. 7 and can be used for this purpose with understanding devices such as pneumatic or hydraulic cylinders, ball screws, or linear electric actuators. When the elevator 140 is lowered, a supply of metal powder “P” having a desired alloy composition can be loaded into the supply container 138. When the elevator 140 is raised, the powder P is exposed on the work surface 128.

  The build platform 120 is a plate-like structure that is slidable vertically below the central opening 130. The build platform 120 is connected to an actuator 121 that is operable to selectively move the build platform 120 up and down. The actuator 121 is shown schematically in FIG. 7 and can be used for this purpose with understanding devices such as pneumatic or hydraulic cylinders, ball screws, or linear electric actuators.

  The overflow container 118 is located below the overflow opening 134 and communicates with the overflow opening 134, and serves as a container for storing excess powder P.

The directional energy source 124 generates any beam of suitable power and other operational characteristics during the build process, as detailed below, and can be any known operable to melt and fuse the metal powder. The device may be provided. For example, the directional energy source 124 may be a laser having a power density on the order of 10 ⁴ W / cm ² . Other directional energy sources such as electron beam guns are suitable alternatives to lasers.

  The beam steering device 126 includes one or more mirrors, prisms, and / or lenses and is provided with suitable actuators to concentrate the beam “B” from the directional energy source 124 to the desired spot size. And is arranged so that it can be directed to a desired position in the XY plane that coincides with the work surface 128.

  As used herein, the term “external thermal control device” maintains the part C positioned on the build platform 120 at an appropriate melting temperature (ie, maintains a predetermined temperature profile), and thus A device other than the directional energy source 124 that is effective in controlling the crystallographic properties of the powder P that solidifies during construction. As will be described in more detail below, the external thermal control device operates by acting directly as a heat source (ie, thermal energy input) or by retaining heat generated by a directional energy heating process. May be.

  Examples of various types of external heat control devices are shown in FIGS. In FIGS. 7 and 8, a layer of insulation 144 surrounds the building enclosure 122. The insulation 144 effectively impedes heat transfer from the part C being built, thereby reducing its cooling rate and maintaining a high temperature.

  9 and 10 illustrate an external thermal control device that includes one or more heaters. The belt-type electric resistance heater 146 wraps the outside of the construction wall 122 and is connected to the power source 148. When turned on, the heater 146 heats the building enclosure 122 (and thus the internal part C) by heat conduction.

  Another optional type of external heat control device is a radiant heat source. For example, FIG. 9 shows a quartz lamp 150 (also referred to as a quartz halogen lamp) that is arranged so that the component C can be seen through and is connected to a power source 152. Such lamps are commercially available, each with a rated output of several thousand watts. When the power is turned on, the quartz lamp 150 heats the component C by radiant heat transfer. The quartz lamp 150 can be used instead of or in addition to the belt-type heater 146 described above.

  Another option for an external thermal controller is induction heating, where the AC current flowing through the induction coil induces a magnetic field, which in turn induces eddy currents in nearby conductive objects, resulting in resistive heating of the objects. In the example shown in FIGS. 11 and 12, the induction heater 154 includes one or more individual induction coils 156 that surround the build platform 120 and are connected to a power source 158. In the illustrated example, a plurality of induction coils 156 are provided. When the power is turned on, the induction heater 154 effectively heats the component C. Experiments by the present inventors have shown that this type of external induction heater 154 does not heat the solidified powder P to the melting or otherwise adhere to the part C without melting / solidifying the powder bed. It has been shown that preferential heating of the part C will be performed.

  The construction process of the part “C” using the above-described apparatus is as follows. The build platform 120 is moved to the initial height position. Optionally, seed element 160 (see FIG. 2) may be initially installed on build platform 120. The seed element 160 serves as a nucleation cooling point and has a selected crystallographic structure. If it is desired to produce a single crystal part C, the seed element will have a single crystal microstructure. Such a seed element 160 can be manufactured by a known technique. Once seed element 160 is in place, build platform 120 is lowered below work surface 128 by the selected layer increment. The layer increment affects the speed and resolution of part C. As an example, the layer increment may be about 10 to 50 micrometers (0.0003 to 0.002 inches). The powder “P” is then placed over the build platform 120 and the seed element 160. For example, the elevator 140 of the supply container 138 may be raised to push powder out of the supply opening 132 and expose it on the work surface 128. The scraper 116 is moved across the work surface to spread the pushed up powder P horizontally across the build platform 120. Any excess powder P falls from the overflow opening 134 to the overflow container 118 as the scraper 116 passes from left to right. Thereafter, the scraper 116 may be returned to the start position.

  A directional energy source 124 is used to melt the two-dimensional cross section of the part C being built. Directional energy source 124 emits beam “B” and uses beam steering device 126 to direct or scan beam B's focal spot “S” against the exposed powder surface in an appropriate pattern. To do. Beam B exposes the exposed layer of powder P to a temperature to melt, fluidize, and solidify the powder.

  The build platform 120 is moved vertically downward by the layer increment and another layer of powder P is covered to a similar thickness. Directional energy source 124 emits beam B again and uses beam steering device 126 to direct or scan beam B's focal spot “S” against the exposed powder surface in an appropriate pattern. . Beam B exposes the exposed layer of powder P to a temperature, causing the powder to melt, fluidize, and solidify with the layer solidified in and before the upper layer.

  This cycle of building platform 120 movement, powder P coating, and subsequent melting of the powder with directional energy is repeated until the entire part C is complete. The scan pattern used is selected such that the negative CTE structure is formed as an integral part of part C.

  The alloy composition of part C need not be uniform. By changing the composition of the powder P during the additive manufacturing process, the composition can be varied to produce various layers or compartments of the part C. For example, the airfoil 18 shown in FIG. 1 includes a radial inner or body portion 17 (below the dotted line) having a first alloy composition, and a second alloy composition that is different from the first alloy composition. May have a radial outer portion or tip portion 19 (above the dotted line).

  If the part C is optionally formed with a single crystal microstructure, this requires controlling the temperature and cooling rate throughout the part C being manufactured. Directional energy heat input is sufficient to maintain the required temperature at the top of part C near where the new layer is actively being built, but not enough for its full range. To address this problem, the method of the present invention uses an external thermal control device during the powder placement and directional energy melting cycle.

  The external thermal control device is operable to control both the temperature and heating rate of the entire part C. For example, one known solution heat treatment includes (1) heating the part to about 1260 ° C. (2300 ° F.) for about 2 hours to homogenize the microstructure, and (2) about 1260 ° C. (2300 ° F.). ) To a solubilization temperature of about 1320 ° C. (2415 ° F.) at a rate of about 5.5 ° C. (10 ° F.) per hour, and then (3) maintain the part at that temperature for about 2 hours And (4) cooling to an aging temperature of about 1120 ° C. (2050 ° F.) within 3 minutes.

  Since the external thermal controller is separate from the directional energy source 124, it can also be used for other heat treatment processes such as aging part C after the build process is complete. For example, one known aging process involves first aging a part for several hours at an aging temperature to achieve the desired microstructure.

  The turbine components described herein are superior to the prior art in several respects. The negative CTE structure offsets part creep and provides tolerance for creep rupture. The negative CTE structure allows even inferior alloys to be used in important engines and exhibit performance, potentially eliminating the need for single crystal materials. The negative CTE structure also serves as part of the thermomechanical system and can lower the bulk temperature of component heat transfer. The negative CTE structure can serve as a turbulent promoter or “turbulator” that is denser than prior art cast turbulators to improve heat transfer. Similarly, the negative CTE structure, when contained within the outer and inner surface walls of the airfoil body, also serves as a heat exchanger and can cool the outer wall more efficiently. .

  Above, a turbine component having a negative CTE structure and a method for manufacturing them have been described. All features disclosed in this specification (including all the appended claims, abstracts, and drawings) and / or any method or process steps so disclosed are all such features and Combinations may be combined in any combination except combinations where at least some of the steps are mutually exclusive.

  Each feature disclosed in this specification (including the appended claims, abstract, and drawings) is an alternative that serves the same, equivalent, or similar purpose unless expressly stated otherwise. Can be replaced with features. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

  The present invention is not limited to the details of the foregoing embodiments. The invention is disclosed as any novel or any novel combination of features disclosed herein (including any attendant potential novelty points, abstracts, and drawings) or as such. Covers any novel or any novel combination of steps of any method or process that has.

10 turbine blade, part 12 dovetail 14 blade shank, shank 16 platform 17 body part 18 hollow airfoil part, airfoil part, gas turbine engine airfoil part 19 tip part 20 base part 22 tip 24 metal wall, concave pressure side wall, pressure side wall , Wall 26 metal wall, convex suction side wall, suction side wall, wall 28 leading edge 30 trailing edge 32 trailing edge cooling hole 34 tip lid 36 upright squealer tip, squealer tip 38 suction side tip wall, tip wall 40 pressure side tip wall, tip Wall 44 Film cooling hole 46 Internal wall 48 Negative CTE structure, hexagonal cell, cell,
50 Negative CTE structure, approximately hourglass shaped cell, cell 52 'wall, convex wall 52 wall, concave wall 54 Negative CTE structure, cell with square shape, cell 63 wall 100 device 112 table 114 powder supply 116 scraper 118 overflow Container 120 Building platform 121 Actuator 122 Building wall 124 Directional energy source 126 Beam steering device 128 Work surface, work plane 130 Central opening 132 Supply opening 134 Overflow opening 136 Actuator 138 Supply container 140 Elevator 142 Actuator 144 Insulation 146 Belt Type electric resistance heater, heater, belt type heater 148 power supply 150 quartz lamp 152 power supply 154 induction heater, external induction heater 156 induction coil 158 power supply 160 seed element 2 8 metal wall, the wall, the component 230 outer layer 232 outer layer 234 negative CTE structure D main dimension or diameter T1 thickness or depth T2 thickness W thickness P metallic powder, powder B beam S focal spot

Claims (16)

Metal walls (24, 26, 228) having opposing inner and outer surfaces and configured to direct the combustion gas flow of a gas turbine engine, and metal rigidly attached to one of said surfaces Turbine component (10) with negative CTE structure (48, 50, 54) made of.   The component (10, 228) of claim 1, wherein the negative CTE structure (48, 50, 54) is rigidly attached to the internal surface.   The component (10, 228) of claim 1, wherein the negative CTE structure is integrally formed with the metal wall (24, 26, 228).   The component (10, 228) of claim 1, wherein the metal wall (24, 26) forms part of a gas turbine engine airfoil (18).   The component (10, 228) according to claim 4, wherein the metal wall (24, 26) is a pressure side wall (24) or a suction side wall (26) of the airfoil.   The component (10, 228) of claim 1, wherein the negative CTE structure comprises a repeating array of hexagonal cells (48).   The negative CTE structure comprises a repetitive two-dimensional array of generally hourglass shaped cells (50), each cell being joined by two spaced concave walls (52 ') joined by two spaced convex walls (52'). 52. The component (10, 228) of claim 1, comprising: 52).   The component (10, 228) of claim 1, wherein the negative CTE structure comprises an iterative two-dimensional array of cells (54) having a rectangular shape.   The component (2) of claim 1, wherein the wall (228) includes opposing spaced outer layers (230, 232) and a negative CTE structure (234) fills a space between the outer layers. 10, 228). A method for producing a part (C, 18, 228), comprising:
Placing the metal powder (P) on the work plane (128);
Directing a beam from a directional energy source (124) to fuse the powder (P) according to a pattern corresponding to a cross-sectional layer of the part (C);
The placement and fusion steps are periodically repeated to build a wall for each layer, the wall (24, 26, 228) having opposing inner and outer surfaces, and the wall (24, 26, 228) being configured to direct the combustion gas flow of the gas turbine engine; and forming a metal negative CTE structure (48, 50, 54) integrally with one of said surfaces. Including methods.   The method of claim 10, wherein the negative CTE structure (48, 50, 54) is fabricated integrally with the internal surface.   The method of claim 10, wherein the walls (24, 26) are pressure sidewalls (24) or suction sidewalls (26) of a gas turbine engine airfoil (18).   The method of claim 10, wherein the negative CTE structure comprises a repeating array of hexagonal cells (48).   The negative CTE structure comprises a repetitive two-dimensional array of generally hourglass shaped cells (50), each cell being joined by two spaced concave walls (52 ') joined by two spaced convex walls (52'). 52. The method of claim 10, comprising: 52).   The method of claim 10, wherein the negative CTE structure comprises an iterative two-dimensional array of cells (54) having a rectangular shape.   The method of claim 10, wherein the wall (228) includes opposing spaced outer layers (230, 232) and a negative CTE structure (234) fills the space between the outer layers.